1. Field of the Invention
The invention relates to a golf club head.
2. Description of the Related Art
The face of a golf club head include a plurality of grooves, known as marking lines, score lines, or face line grooves (hereinafter referred to as score line grooves), which affect the amount of spin on a ball. It is desirable to have the grooves on an iron club head, especially a wedge, in order to increase the amount of spin on the ball.
Japanese Patent Application Laid-Open No. 9-192274 discloses a golf club having grooves of V-shaped or trapezoidal cross section. Japanese Patent Application Laid-Open No. 9-70457 and No. 10-179824 disclose a golf club head with rounding on the edges of the score line groove, that is, where the score line grooves meets the face. The rounding has the effect of avoiding scratching or other damage to the ball. Japanese Patent Laid-Open No. 2003-93560 and No. 2005-287534 disclose a golf club head having score line grooves each of which has a side surface with two varying angles, such that the side surface is not constituted on a single, flat plane. Rules of golf regulate width and depth of score line grooves on a golf club head used in official competition play, and steps must be taken that satisfy the pertinent rules when considering applications in official play.
The amount of spin on the ball affects the surface roughness of the face as well. Japanese Patent Laid-Open No. 2005-169129 discloses a golf club head with a face having the surface roughness of not less than 40 Ra. Japanese Patent No. 3,000,921 discloses a golf club head with a face having a plurality of fine grooves that are distinct from the score line grooves. Rules of golf regulate roughness of a face on a golf club head used in official competition play, and steps must be taken that satisfy the pertinent rules when considering applications in official play.
Spin on a ball tends to decline when hitting in bad weather or in the rough, compared with hitting in fair weather or on the fairway. Increasing the volume of the score line grooves is one method of avoiding reduction in spin when hitting in bad weather or in the rough. Increasing the volume of the score line grooves makes it easier to get rid of grass and dirt that may be caught between the face and the ball into the score line grooves, and also improves drainage performance on the face.
Score line grooves with square cross-sectioning tends to have larger volume than score line grooves with other cross-sectioning, presuming an identical width, at the cost of increased damage to the ball, owing to a sharper angle on the edges of the score line groove.
Score line grooves with a V-shaped or trapezoidal cross-section may minimize damage to the ball, at the expense of reduced score line grooves volume, which tends to significantly reduce spin when hitting in bad weather or in the rough.
The golf club head disclosed in Japanese Patent Laid-Open No. 2003-93560 has score line groove edges with sharp angles that cause greater damage to the ball. The golf club head disclosed in Japanese Patent Laid-Open No. 2005-287534 may be unworkable, owing to the width of the interior of the score line groove being wider than the score line groove in the face. The score line groove edges also have sharp angles that cause greater damage to the ball. While Japanese Patent Laid-Open No. 2005-287534 discloses a golf club head with rounding on the edges of the score line groove, score line groove edges with significantly sharp angles, such as the score line grooves in Japanese Patent Laid-Open 2005-287534, may cause greater damage to the ball even if the edges are rounded. Even if the surface roughness of the face is modified, such as with the golf club heads disclosed in Japanese Patent Laid-Open No. 2005-169129 and Japanese Patent No. 3,000,921, poor drainage performance on the face will reduce spin.